Comparison between Measurements and Predictions of Fan Broadband Noise on a Low Speed Fan Rig

Abstract

This paper presents a comparison between measurements and predictions of the fan broadband noise in a low speed fan rig. It is assumed here that the broadband noise is due to the interaction between turbulence generated in the wake of the rotor and the downstream stator vanes. The contribution due to the background turbulence level is also included in the analysis. The stator vanes are assumed to be unloaded flat plates and the wakes are assumed to satisfy two-dimensional plane wake theory. The wake turbulence velocity correlation function is assumed to be periodic in the blade pitch direction (i.e., cyclo-stationary). Aerodynamic input data to the model, both steady and unsteady, is taken directly from hot wire velocity measurements. Comparisons between predicted and measured sound power spectra are in reasonable agreement with spectral shape being particularly well captured by the model. We first review the details of the broadband noise prediction model. Hot wire velocity data will then presented by way of validating the model simplifying assumptions, and to provide the input data to the model. Finally, comparisons between the measured and predicted sound power spectrum will be presented. The work reported here was undertaken as part of the European project, PROBAND.